The present invention relates to the control of gear changes in an automatic transmission for a motor vehicle. More particularly, it pertains to a strategy for controlling gear changes following a change-of-mind event in a powershift transmission.
A change-of-mind shift occurs when the operator of a motor vehicle equipped with an automatic transmission depresses the accelerator pedal, called a “tip-in,” and immediately releases the pedal, called a “tip-out” or “back-out.” A change-of-mind shift can occur also when the vehicle operator releases the accelerator pedal, then immediately depresses the pedal. If the transmission were operating in third gear when the change-of-mind event occurs, an upshift through several gears to sixth gear might be immediately followed by a downshift to third gear. Change-of-mind gear shifts are very difficult to handle in a powershift transmission, and they require a relatively long period to complete due to the need for coordinated engagement and disengagement of several synchronizers or couplers during the shift. In some cases, the transmission performs a single upshift, such as a 6-3 shift, when the driver tips-in. Such shifts cause the operator to sense a lengthy, unacceptable delay in completing the shift, and the shift may be accompanied by a bump or harsh shift feel. Vehicle occupants regard such sensations as unacceptable shift quality.
There is a need promptly to stabilize gear changes in a powershift transmission following a change-of-mind event. There is a need to eliminate harshness and delay in completing gear changes following the event that initiates automatic gear changes in the transmission.